On behalf of manatees — which are actually named as the plaintiffs in the case — two other animal species and the chairman of an environmental group, attorneys filed a 60-day notice of intent to sue state health officials Thursday over septic tank waste that has polluted the Indian River Lagoon on Florida's east coast.

Hundreds of manatees, dolphins and pelicans have died in the lagoon, once considered one of the most productive estuaries in North America. The deaths were preceded by toxic algae blooms that wiped out more than 47,000 acres of its sea grass beds, which one scientist compared to losing an entire rainforest in one fell swoop.

Fueling the algae blooms and darkening the lagoon's once clear waters are rising amounts of nutrient pollution, the result of fertilizer in storm runoff and leaking septic tanks.

Thirty years of state and federal reports show the connection between the septic tanks and the pollution in the lagoon, said Christopher Byrd, one of two lawyers who filed the notice of intent letter.

The notice letter is not a lawsuit, but rather a way to get a government agency to negotiate to avoid one. In the letter, the two lawyers call for state health officials "to immediately cease the issuance of septic tank authorizations in the Indian River Lagoon drainage basin."

They also want the state Department of Health to find and fix any septic tanks that are leaking into the lagoon.

Health department spokeswoman Sheri Hutchinson said the letter has been referred to the agency's legal staff, but she said, "The department has been an active partner in discussions regarding the Indian River Lagoon and has taken all necessary steps to protect the public health."

So far scientists have been unable to show a direct link between the pollution in Indian River Lagoon and the deaths of the manatees, dolphins and pelicans. But Byrd said the pollution has definitely harmed the habitat of endangered species, which is what matters under federal law.

The notice of intent letter says the Health Department's continued septic tank permitting violates the Endangered Species Act because of the effect on manatees and two other endangered species, the green sea turtle and the Atlantic salt marsh snake.

The letter says it has also hurt the livelihood of Cocoa Beach eco-tour guide Tim Chastain, who is also founding chairman of the local chapter of the Surfrider Foundation and is their other client.

Whether there's a lawsuit or not, "we're hoping to bring real change to the way people think about their waste," Byrd said.

He said he wishes someone had stepped in long ago to save the Indian River Lagoon the way the Tampa Bay Estuary Program was able to curtail septic tank pollution in its area, reviving sea grass beds and improving the bay's overall health.

Craig Pittman can be reached at craig@tampabay.com. Follow him @craigtimes on Twitter.